arXiv subjects

Soebur Razzaque

Publications and source records attributed to Soebur Razzaque.

At least 73 records · Page 4Linked to original sources

arXiv2016

Photodisintegrated gamma rays and neutrinos from heavy nuclei in the gamma-ray burst jet of GRB 130427A

Detection of ~ 0.1-70 GeV prompt gamma-ray emission from the exceptionally bright gamma-ray burst (GRB) 130427A by the Fermi-Large Area Telescope provides an opportunity to explore the physical processes of GeV gamma-ray emission from the GRB jets. In this work we discuss interactions of Iron and Oxygen nuclei with observed keV-MeV photons in the jet of GRB 130427A in order to explain an additional, hard spectral component observed during 11.5-33 second after trigger. The photodisintegration time scale for Iron nuclei is comparable to or shorter than this duration. We find that gamma rays resulting from the Iron nuclei disintegration can account for the hard power-law component of the spectra in the 1-70 GeV range, before the gamma-gamma to electron-positron pair production with low-energy photons severely attenuates emission of higher energy photons. Electron antineutrinos from the secondary neutron decay, on the other hand, can be emitted with energies up to 2 TeV. The flux of these neutrinos is low and consistent with non-detection of GRB 130427A by the IceCube Neutrino Observatory. The required total energy in the Iron nuclei for this hadronic model for GeV emission is approximately 10 times the observed total energy released in the prompt keV-MeV emission.

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arXiv2015

Angular correlation of cosmic neutrinos with ultrahigh-energy cosmic rays and implications for their sources

Cosmic neutrino events detected by the IceCube Neutrino Observatory with energy $\gtrsim 30$ TeV have poor angular resolutions to reveal their origin. Ultrahigh-energy cosmic rays (UHECRs), with better angular resolutions at $>60$ EeV energies, can be used to check if the same astrophysical sources are responsible for producing both neutrinos and UHECRs. We test this hypothesis, with statistical methods which emphasize invariant quantities, by using data from the Pierre Auger Observatory, Telescope Array and past cosmic-ray experiments. We find that the arrival directions of the cosmic neutrinos are correlated with $\ge 100$ EeV UHECR arrival directions at confidence level $\approx 93\%$. The strength of the correlation decreases with decreasing UHECR energy and no correlation exists at energy $\sim 60$ EeV. A search in astrophysical databases within $3^\circ$ of the arrival directions of UHECRs with energy $\ge 100$ EeV, that are correlated with the IceCube cosmic neutrinos, resulted in 18 sources from the Swift-BAT X-ray catalog with redshift $z\le 0.06$. We also found 3 objects in the Kühr catalog of radio sources using the same criteria. The sources are dominantly Seyfert galaxies with Cygnus A being the most prominent member. We calculate the required neutrino and UHECR fluxes to produce the observed correlated events, and estimate the corresponding neutrino luminosity (25 TeV-2.2 PeV) and cosmic-ray luminosity (500 TeV-180 EeV), assuming the sources are the ones we found in the Swift-BAT and Kühr catalogs. We compare these luminosities with the X-ray luminosity of the corresponding sources and discuss possibilities of accelerating protons to $\gtrsim 100$ EeV and produce neutrinos in these sources.

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arXiv2015

A multi-messenger study of the Fermi Bubbles: very high energy gamma rays and neutrinos

The Fermi Bubbles have been imaged in sub-TeV gamma rays at Fermi-LAT, and, if their origin is hadronic, they might have been seen with low statistics in $\sim 0.1- 1$ PeV neutrinos at IceCube. We discuss the detectability of these objects at the new High Altitude Water Cherenkov (HAWC) gamma ray detector. HAWC will view the North Bubble for $\sim 2-3$ hours a day, and will map its spectrum at 0.1-100 TeV. For the hard primary proton spectrum required to explain five events at IceCube, a high significance detection at HAWC will be achieved in less than 30 days. The combination of results at HAWC and IceCube will substantiate the hadronic model, or constrain its spectral parameters.

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arXiv2015

Super-PINGU for measurement of the leptonic CP-phase with atmospheric neutrinos

We explore a possibility to measure the CP-violating phase $δ$ using multi-megaton scale ice or water Cherenkov detectors with low, $(0.2 - 1)$ GeV, energy threshold assuming that the neutrino mass hierarchy is identified. We elaborate the relevant theoretical and phenomenological aspects of this possibility. The distributions of the $ν_μ$ (track) and $ν_e$ (cascade) events in the neutrino energy and zenith angle $(E_ν- θ_z)$ plane have been computed for different values of $δ$. We study properties and distinguishability of the distributions before and after smearing over the neutrino energy and zenith angle. The CP-violation effects are not washed out by smearing, and furthermore, the sensitivity to $δ$ increases with decrease of the energy threshold. The $ν_e$ events contribute to the CP-sensitivity as much as the $ν_μ$ events. While sensitivity of PINGU to $δ$ is low, we find that future possible upgrade, Super-PINGU, with few megaton effective volume at ($0.5 - 1$) GeV and e.g. after 4 years of exposure will be able to disentangle values of $δ= π/2,~ π,~ 3π/2$ from $δ= 0$ with "distinguishability" ($\sim$ significance in $σ$'s) $S_σ^{tot} = (3 - 8),~ (6 - 14),~(3 - 8)$ correspondingly. Here the intervals of $S_σ^{tot}$ are due to various uncertainties of detection of the low energy events, especially the flavor identification, systematics, {\it etc.} Super-PINGU can be used simultaneously for the proton decay searches.

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arXiv2015

Spectral Studies of Flaring FSRQs at GeV Energies Using Pass 8 Fermi-LAT Data

Flat spectrum radio quasars (FSRQs) are bright active galactic nuclei surrounded by gas clouds within a UV-visible intense radiation field that form the so-called broad line region (BLR). These objects emit relativistic jets from a region close to the central supermassive black hole and through the BLR. The Fermi-Large Area Telescope (Fermi-LAT) is sensitive to gamma-ray photons from $\sim$30 MeV to more than 300 GeV. We have performed spectral analysis of bright FSRQs in a 5.5 year (2008-2014) data sample collected by Fermi-LAT, using the new Pass 8 event selection and instrument response function. Also, our study of flaring episodes in a limited time range brings interesting results while compared to the full 5.5 year data samples.

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arXiv2015

PeV-EeV neutrinos from GRB blastwave in IceCube and future neutrino telescopes

Ultrahigh-energy cosmic rays (UHECRs), if accelerated in the gamma-ray burst (GRB) blastwave, are expected to produce PeV-EeV neutrinos by interacting with long-lived GRB afterglow photons. Detailed spectral and temporal properties of the flux of these neutrinos depend on the GRB blastwave evolution scenario, but can last for days to years time scale in contrast to the seconds to minutes time scale for "burst" neutrino flux contemporaneous with the prompt gamma-ray emission and which has been constrained by IceCube in the $\sim$ 50 TeV-2 PeV range. We compute expected neutrino events in IceCube in the PeV-EeV range from the blastwave of long-duration GRBs, both for the diffuse flux and for individual GRBs in the nearby universe. We show that IceCube will be able to detect the diffuse GRB blastwave neutrino flux after 5 years of operation, and will be able to distinguish it from the cosmogenic neutrino flux arising from GZK process in case the UHECRs are heavy nuclei. We also show that EeV neutrinos from the blastwave of an individual GRB can be detected with long-term monitoring by a future high-energy extension of IceCube for redshift up to $z\sim 0.5$.

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arXiv2015

Super-PINGU for measuring CP violation

We propose to measure leptonic CP phase, after neutrino mass hierarchy is established, with an upgrade of the PINGU detector and using atmospheric neutrino flux. The upgrade, called super-PINGU, will require a few megaton effective volume at 0.5-1 GeV range to distinguish $δ$ in the range $π/2$-$3π/2$ from 0 after 4 years of operation. The distinguishability (similar to significance) of measuring $δ$ depends crucially on various flux, cross-section, event reconstruction (energy and angle) and flavor identification uncertainties. We explore effects of these uncertainties on the distinguishability of measuring CP phase and suggest possible ways to minimize their impact.

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arXiv2014

IceCube Neutrino Events from Fermi Bubbles

The IceCube Neutrino Observatory announced thirty-seven candidate events observed with deposited energies above $\sim$ 30 TeV with three-year dataset, more than expected from atmospheric backgrounds. We discuss the detectability of the Fermi Bubbles (FB) by IceCube and show that up to 6 -- 7 of the 37 events could originate from the FB. If the observed gamma rays from the FB are created due to baryonic mechanism, high-energy ($>$ GeV) neutrinos should be emitted as a counterpart. These neutrinos should be detectable as shower- or track-like events at a Km$^3$ neutrino detector. For a hard primary cosmic-ray proton spectrum, $E^{-2.1}$, and cutoff energy at or above 10 PeV, the FB flux substantially exceeds the atmospheric backgrounds. For a steeper spectrum, $E^{-2.3}$, and/or lower cutoff energy, detection with high significance will require a longer running time.

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arXiv2014

Neutrino Events at IceCube and the Fermi Bubbles

We discuss the possibility that the IceCube neutrino telescope might be observing the Fermi Bubbles. If the bubbles discovered in gamma rays originate from accelerated protons, they should be strong emitters of high energy (> GeV) neutrinos. These neutrinos are detectable as shower- or track-like events at a Km^3 neutrino observatory. For a primary cosmic ray cutoff energy at or above 10 PeV, the Fermi Bubble flux substantially exceeds the atmospheric background, and could account for up to ~ 4-5 of the 28 events detected above ~ 30 TeV at IceCube. Running the detector for ~ 5-7 more years should be sufficient to discover this flux at high significance. For a primary cosmic ray flux with steeper spectrum, and/or lower cutoff energy, longer running times will be required to overcome the background.

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arXiv2013

Long-lived PeV-EeV Neutrinos from GRB Blastwave

Long duration gamma-ray bursts are powerful sources that can accelerate particles to ultra-high energies. Acceleration of protons in the forward shock of the highly relativistic GRB blastwave allows PeV--EeV neutrino production by photopion interactions of ultra-high energy protons with X-ray to optical photons of the GRB afterglow emission. Four different blastwave evolution scenarios are considered: adiabatic and fully radiative blastwaves in a constant density circumburst medium and in a wind environment with the particle density in the wind decreasing inversley proportional to the square of the radius from the center of the burst. The duration of the neutrino flux depends on the evolution of the blastwave, and can last up to a day in the case of an adibatic blastwave in a constant density medium. Neutrino fluxes from the three other blastwave evolution scenarios are also calculated. Diffuse neutrino fluxes calculated using the observed rate of long-duration GRBs are consistent with the recent IceCube upper limit on the prompt GRB neutrino flux below PeV. The diffuse neutrino flux needed to explain the two neutrino events at PeV energies recently detected by IceCube can partially come from the presented GRB blastwave diffuse fluxes. Future observations by IceCube and upcoming huge radio Askaryan experiments will be able to probe the flux models presented here or constrain the GRB blastwave properties.

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arXiv2013

Hints of an axion-like particle mixing in the GeV gamma-ray blazar data?

Axion-Like Particles (ALPs), if exist in nature, are expected to mix with photons in the presence of an external magnetic field. The energy range of photons which undergo strong mixing with ALPs depends on the ALP mass, on its coupling with photons as well as on the external magnetic field and particle density configurations. Recent observations of blazars by the Fermi Gamma-Ray Space Telescope in the 0.1-300 GeV energy range show a break in their spectra in the 1-10 GeV range. We have modeled this spectral feature for the flat-spectrum radio quasar 3C454.3 during its November 2010 outburst, assuming that a significant fraction of the gamma rays convert to ALPs in the large scale jet of this blazar. Using theoretically motivated models for the magnetic field and particle density configurations in the kiloparsec scale jet, outside the broad-line region, we find an ALP mass $m_a\sim (1-3)\cdot 10^{-7}$ eV and coupling $g_{aγ} \sim (1-3)\cdot 10^{-10}$ GeV$^{-1}$ after performing an illustrative statistical analysis of spectral data in four different epochs of emission. The precise values of $m_a$ and $g_{aγ}$ depend weakly on the assumed particle density configuration and are consistent with the current experimental bounds on these quantities. We apply this method and ALP parameters found from fitting 3C454.3 data to another flat-spectrum radio quasar PKS1222+216 (4C+21.35) data up to 400 GeV, as a consistency check, and found good fit. We find that the ALP-photon mixing effect on the GeV spectra may not be washed out for any reasonable estimate of the magnetic field in the intergalactic media.

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arXiv2013

The Galactic Center Origin of a Subset of IceCube Neutrino Events

The center of the Milkyway is a host to energetic phenomena across many electromagnetic wave-bands and now possibly of high-energy neutrinos. We show that 5 out of 21 IceCube shower-like events, including a PeV event, likely originated from the Galactic Center region. Hard spectrum and flux inferred from these events are inconsistent with atmospheric neutrinos. The flux of these neutrinos is consistent with an extrapolation of the gamma-ray flux measured by Fermi-LAT from the inner Galactic region. This indicates a common hadronic origin of both, powered by supernovae. Three other shower-like events are spatially correlated with the Fermi bubbles, originating from the Galactic Center activity, within the uncertainty of reconstructing their arrival directions. Origin of the other neutrino events, including 7 track-like events, is still elusive.

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arXiv2013

Mass hierarchy, 2-3 mixing and CP-phase with Huge Atmospheric Neutrino Detectors

We explore the physics potential of multi-megaton scale ice or water Cherenkov detectors with low ($\sim 1$ GeV) threshold. Using some proposed characteristics of the PINGU detector setup we compute the distributions of events versus neutrino energy $E_ν$ and zenith angle $θ_z$, and study their dependence on yet unknown neutrino parameters. The $(E_ν- θ_z)$ regions are identified where the distributions have the highest sensitivity to the neutrino mass hierarchy, to the deviation of the 2-3 mixing from the maximal one and to the CP-phase. We evaluate significance of the measurements of the neutrino parameters and explore dependence of this significance on the accuracy of reconstruction of the neutrino energy and direction. The effect of degeneracy of the parameters on the sensitivities is also discussed. We estimate the characteristics of future detectors (energy and angle resolution, volume, etc.) required for establishing the neutrino mass hierarchy with high confidence level. We find that the hierarchy can be identified at $3σ$ -- $10σ$ level (depending on the reconstruction accuracies) after 5 years of PINGU operation.

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arXiv2013

Gamma Ray Bursts in the Swift-Fermi Era

Gamma-ray bursts (GRBs) are among the most violent occurrences in the universe. They are powerful explosions, visible to high redshift, and thought to be the signature of black hole birth. They are highly luminous events and provide excellent probes of the distant universe. GRB research has greatly advanced over the past 10 years with the results from Swift, Fermi and an active follow-up community. In this review we survey the interplay between these recent observations and the theoretical models of the prompt GRB emission and the subsequent afterglows.

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arXiv2012

High Energy Neutrinos from the Fermi Bubbles

Recently the Fermi-LAT data have revealed two gamma-ray emitting bubble-shaped structures at the Galactic center. If the observed gamma rays have hadronic origin (collisions of accelerated protons), the bubbles must emit high energy neutrinos as well. This new, Galactic, neutrino flux should trace the gamma ray emission in spectrum and spatial extent. Its highest energy part, above 20-50 TeV, is observable at a kilometer scale detector in the northern hemisphere, such as the planned KM3NeT, while interesting constraints on it could be obtained by the IceCube Neutrino Observatory at the South pole. The detection or exclusion of neutrinos from the Fermi bubbles will discriminate between hadronic and leptonic models, thus bringing unique information on the still mysterious origin of these objects and on the time scale of their formation.

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arXiv2012

Searches for sterile neutrinos with IceCube DeepCore

We show that study of the atmospheric neutrinos in the 10--100 GeV energy range by DeepCore sub-array of the IceCube Neutrino Observatory can substantially constrain the mixing of sterile neutrinos of mass $\sim 1$ eV with active neutrinos. In the scheme with one sterile neutrino we calculate $ν_μ-$ and $\barν_μ-$ oscillation probabilities as well as zenith angle distributions of $ν_μ^{CC}$ events in different energy intervals in DeepCore. The distributions depend on the mass hierarchy of active neutrinos. Therefore, in principle, the hierarchy can be identified, if $ν_s$ exists. After a few years of exposure the DeepCore data will allow to exclude the mixing $|U_{μ4}|^2 \geq 0.02$ indicated by the LSND/MiniBooNE results. Combination of the DeepCore and high energy IceCube data will further improve sensitivity to $ν_s$ mixing parameters.

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arXiv2012

The next-generation liquid-scintillator neutrino observatory LENA

We propose the liquid-scintillator detector LENA (Low Energy Neutrino Astronomy) as a next-generation neutrino observatory on the scale of 50 kt. The outstanding successes of the Borexino and KamLAND experiments demonstrate the large potential of liquid-scintillator detectors in low-energy neutrino physics. LENA's physics objectives comprise the observation of astrophysical and terrestrial neutrino sources as well as the investigation of neutrino oscillations. In the GeV energy range, the search for proton decay and long-baseline neutrino oscillation experiments complement the low-energy program. Based on the considerable expertise present in European and international research groups, the technical design is sufficiently mature to allow for an early start of detector realization.

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arXiv2011

Lower limits on ultrahigh-energy cosmic ray and jet powers of TeV blazars

Lower limits on the power emitted in ultrahigh-energy cosmic rays (UHECRs), which are assumed to be protons with energy 1e17-1e20 eV, are derived for TeV blazars with the assumption that the observed TeV gamma rays are generated due to interactions of these protons with cosmic microwave photons. The limits depend on the spectrum of the injected UHECR protons. While for a -2.2 injection spectrum, the lower limits on the powers emitted in UHECRs by 1ES 0229+200, 1ES 1101-232 and 1ES 0347-121 are lower than their respective synchrotron luminosities (1e46 erg/s); in the case of 1ES 1426+428 it exceeds the corresponding synchrotron luminosity by up to an order of magnitude. The proposed Auger North Observatory should be able to detect 4e19 eV cosmic ray protons from 1ES 1426+428 within a few years of operation and test the TeV gamma-ray production model by UHECR energy losses while propagating along the line-of-sight, or constrain the intergalactic magnetic field to be larger than 1e-16 G in case of no detection. The lower limits on the apparent-isotropic jet power from accelerated 1e10-1e20 eV proton spectra in the blazar jet is of the order of the Eddington luminosity of a 1e9 solar mass black hole for a cosmic-ray injection spectrum -2.2 or harder for all blazars considered except for 1ES 1426+428. In the case of the latter the apparent-isotropic jet power exceeds the Eddington luminosity by an order of magnitude. For an injection spectrum softer than -2.2, as is required to fit the observed cosmic-ray data above 1e17-1e18 eV, the Eddington luminosity is exceeded by the lower limits on the jet power for all blazars considered.

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